Bats Use Echo Templates to Recognize Key Places

How bats navigate at night while foraging is pretty well understood. They use echolocation, emitting high-pitched sounds and then using the return echoes to perceive objects mapped out in their midst -- from trees to boulders to tasty insects.

But the ability to follow a route -- say to a roosting spot or favorite feeding site -- requires recognition of places along the way, and what's not so well understood is how bats use echolocation to manage that feat.

Researchers from the University of Bristol and the University of Antwerp thought bats might be using a kind of template-based system for navigation, in which places were remembered by specific echo signatures instead of 3-D echolocation layouts, so they set out to test the idea.

How do you test whether bats likely use echo signatures as place templates? The scientists in this study built their own bat, one complete with ultrasonic microphone "ears," speaker "mouth" and computer brain to store measurement data.

This artificial bat boasted ultrasonic microphones and speakers to act as ears and a mouth, to gather echoes from different locations and assess the templates from the data. Credit: Vanderelst et al., eLife, 2016

The researchers collected calls and echoes their artificial bat made over different types of terrain and then analyzed what kind of sonic templates might emerge.

It turned out that the echoes returned from each place to their fake bat were indeed unique enough to be considered templates that represented specific locations.

Here's the 'bat' in action, in a park in Israel. The echo catchment distances were greater in this corridor of boulders than in the corridor of vegetation in the Royal Fort Gardens, suggesting that bats can use boulders and other such landmarks for mapping. Credit: Vanderelst et al., eLife

"Importantly, our method used the echoes without inferring the location or identity of objects, such as plants and trees, at each site," noted study co-author Dieter Vanderelst, of the University of Antwerp, in a statement.

"In other words," he said, "the data support our hypothesis that bats can recognize places by remembering how they sound, rather than how they appear through the animals' 3-D sonar imaging."

The types of terrain over which their artificial bat "flew" varied between lush, leafy parks and gardens in the UK and stony, more spacious lands of a park in Israel.

The different terrain setups helped the scientists observe that stronger, more recognizable features, such as boulders in the park in Israel, returned more recognizable echo signatures and that such features could serve as landmarks for the animals on their journeys.

"With these new insights in mind," said Vanderelst, "our aim is to try and piece together the entire puzzle of the navigation tendencies and capabilities in bats."

Did you know April 17 is bat appreciation day? And why not? These flying mammals, though they look a bit scary to some people, are actually most welcome critters, for all of the good they do.
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